Lesson 15: Creating Excel VBA Functions.

15.1 Creating Excel VBA Functions

You can create your own functions to complement the built-in functions in Microsoft Excel spreadsheet, which are quite limited in some aspects. These user-defined functions are also called Visual Basic for Applications functions, or simply VBA functions. They are very useful and powerful if you know how to program them properly. One main reason we need to create user defined functions is to enable us to customize our spreadsheet environment for individual needs. For example, we might need a function that could calculate commissions payment based on the sales volume, which is quite difficult if not impossible by using the built-in functions alone.

Table 15.1: Commissions Payment Table

Sales Volume($)	Commissons
<500	3%
<1000	6%
<2000	9%
<5000	12%
>5000	15%

In table 15.1, when a salesman attains a sale volume of  $6000, he will be paid $6000x15%=$720.00. A visual basic function to calculate the commissions can be written as follows:

Function Comm(Sales_V  As Variant) as Variant

If Sales_V <500 Then
Comm=Sales_V*0.03
Elseif Sales_V>=500 and Sales_V<1000 Then
Comm=Sales_V*0.06
Elseif Sales_V>=1000 and Sales_V<2000 Then
Comm=Sales_V*0.09
Elseif Sales_V>=200 and Sales_V<5000 Then
Comm=Sales_V*0.12
Elseif Sales_V>=5000  Then
Comm=Sales_V*0.15
End If

End Function

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15.2 Using Microsoft Excel Visual Basic Editor

To create VBA functions in MS Excel, you can  click on tools, select macro and then click on Visual Basic Editor as shown in Figure 15.1
 

Figure 15.1: Inserting MS_Excel Visual Basic Editor

Upon clicking the Visual Basic Editor, the VB Editor windows will appear as shown in figure 15.2. To create a function, type in the function as illustrated in section 15.1 above After typing, save the  file and then return to the Excel windows.
In the Excel window, type in the titles Sales Volume and Commissions in any two cells. By referring to figure 15.3, key-in the Comm function at cell C4 and by referencing the value in cell B4, using the format Comm(B4). Any value appear in cell B4 will pass the value to the Comm function in cell C4. For the rest of the rows, just copy the formula by  dragging  the bottom right corner of cell C4 to the required cells, a nice and neat table that shows the commissions will automatically appear (as shown in figure 15.3). It can also be updated anytime.

Figure 15.2 : The VB Editor

Figure 15.3: MS Excel Windows- Sales Volume

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